Coatings are applied to aircraft for a variety of reasons, including protection of paint layers, prevention of corrosion, reduction of radar signatures, screening from infrared or ultraviolet radiation, shedding of ice, and so on. An emerging area of coatings technology is smart coatings which have self-healing or sensing capabilities.
Composite materials have become widely used in a variety of aircraft aerospace and military applications including aircraft bodies, missile cones, and similar applications. A problem associated with composites is the potential for damage either by extreme temperature or by object impact and resulting delamination or cracking, which may not be easily detected without sophisticated non-destructive techniques such as ultrasonic inspection, x-ray microscopy, microscopic evaluation, infrared inspection and other spectroscopic techniques.
The coating used to protect the composite is itself recognized to be a possible means of detecting damage and visually assessing whether or not conduct a repair or simply consider further evaluation. One version of such a coating is believed to have been developed by LUNA Innovations and employs encapsulated dyes which break under impact to the coating to create visually perceptible indicators of damage. The aforementioned coatings which employ microencapsulated dyes to indicate the severity and point of impact in such a way that opaque color spots develop due to the leakage of dye from fractured microcapsules have significant limitations in (a) temperature and impact energy thresholds prior to indication of damage, (b) the strength and speed of the color development, as well as (c) being susceptible to the normal stability limits of organic dyes, particularly ultra-violet (UV) instability.
An object of the present invention is to provide smart “nano” coatings for detecting damage by employing a coating which will indicate thermal or mechanical stress by a color change.
Another object of the present invention is to provide methods of use for smart coatings that can indicate thermal and/or mechanical stress.